1. Field of the Invention
The present invention relates to an endoscope for use in observation of internal tissue of a living body under examination or an endoscope for industrial use and, more particularly, to an endoscope which has a device that displays the bending state of a bending section provided at the distal end of its insertion section.
2. Description of the Prior Art
A typical endoscope has an insertion section and an operating section and permits a bending section provided at the distal end of the insertion section to be bent in the desired direction through manual operation of a bending manipulation wire that is disposed within the insertion section.
Recently, in place of the above manual-operation type endoscope, different type of endoscopes have been developed which have a motor assembled within the operating section as a driving device to operate the bending manipulation wire in the insertion section, or which have a shape memorizable alloy disposed within the insertion section and permit the bending section to be bent by heating the shape memorizable alloy.
With the mechanical driving type of endoscopes, unlike the manual operation type, an operator cannot feel, through his or her hands, how much the bending section has been bent.
To cope with this problem, therefore, as disclosed in Japanese Utility Model Disclosure No. 60-106601 and Japanese Patent Disclosure No. 61-79439, for example, a device has been proposed which detects a bent angle of the bending section from the length of the bending manipulation wire moved.
However, if the endoscope's insertion section, when inserted into a body, bends along the body interior wall, the length of the bending manipulation wire moved does not coincide with the moved length of the wire in the case where the insertion section is inserted without bending. In this case, therefore, it is difficult for the above-mentioned bent-angle detecting device to accurately detect the bent angle of the bending section. For instance, even with the moved length of the bending manipulation wire being the same for both cases, if portion of the insertion section is bent, the bent angle of the bending section would change. Specifically, the wire that bends with bending of the insertion section absorbs the tension at the operating section and stretches due to the tensile strength caused by the bending of the insertion section. As a result, it is difficult to accurately detect the bent angle of the bending section.